A display panel includes an array substrate and an opposite substrate aligned and combined with the array substrate to form a cell. During a general manufacturing of display panel, it is required to prepare a thin film transistor, a pixel electrode, a signal line and other structures on the array substrate, and prepare a color filter, a black matrix and other structures on the opposite substrate first. Then, the array substrate (or the opposite substrate) is provided with spacers thereon and coated with a sealant on edges thereof, the array substrate is aligned and combined with the opposite substrate, and liquid crystal is injected therebetween. In this way, a display panel is completely prepared.
During the aforementioned preparation process, due to some factors such as different heights of the spacers, non-uniform thickness of the sealant coated in regions of the edges, and deviation occurred in the aligning and combining process of the array substrate and the opposite substrate, the display panel obtained after the array substrate is aligned and combined with the opposite substrate is prone to have poor flatness. Hence, after the display panel is completely prepared, it is required to detect the flatness of the surface of the display panel.
Particularly for a touch display panel of an On-Cell type, during the preparation process, it is required to perform deposition, coating, exposure, developing, etching and other processes after the array substrate is aligned and combined with the opposite substrate, so as to prepare a touch electrode on the side of the opposite substrate, thus realizing a touch operation. During the exposure, the poor flatness of the surface of the display panel easily results in misalignment in exposure. As a result, the shape and precision of the touch electrode will be influenced. Hence, for a touch display panel of the On-Cell type, it is more required to detect the flatness of the surface of the display panel obtained after the array substrate is aligned and combined with the opposite substrate, prior to the formation of the touch electrode, so as to prevent the poor flatness from influencing the subsequent formation of the touch electrode.
In the prior art, the flatness of the surface of the display panel is generally detected by using a probe to scratch the surface of the display panel. However, in the aforementioned detection method, the probe comes into contact and rubs with the display panel. In this way, the display panel is likely to have scratches thereon, and powder/particles and other pollutants may be produced, thereby damaging the display panel and destroying the cleanliness of the display panel.